sedimentary

Tumbled gray-green pebble, likely chert or altered volcanic rock

Cryptocrystalline quartz (chert), possibly silicified volcanic material

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; pale gray-green to tan, smooth water-worn surface, dull to weakly waxy luster, and no visible cleavage. The opaque body and tiny dark inclusions are consistent with chert, though the photograph cannot exclude fine-grained basalt or altered rhyolite.

Identified August 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed by silica replacement or deposition, then rounded by stream or beach transport; its exact geological age cannot be determined visually. Near 48.5°N, 122.3°W, glacial and stream gravels commonly contain transported chert and volcanic rocks.

Uses & applications

Usually a collecting specimen or tumbled stone; chert can be used for flaked tools and minor aggregate, but this small piece has little commercial value.

Geological facts

A glassy fracture or ability to scratch ordinary glass would support chert. A stronger green color, abundant tiny crystals, or magnetic response could indicate an altered volcanic alternative.

Field identification & locations

Test inconspicuously: chert should scratch glass and resist a steel knife; it should not fizz with dilute acid. Likely source areas include glacial gravels, river deposits, and beaches of the Pacific Northwest.